1. Field of the Invention
The present invention relates to dielectric ceramic compositions for microwave application and, more particularly, to dielectric ceramic compositions for microwave devices such as, for example, those having a dielectric resonator designed to operate in a microwave frequency range of 10 GHz above.
2. Discussion of Related Art
Recently, telecommunications such as mobile communication and satellite communication have focused a growing interest in dielectric ceramic devices for microwave application. In particular, mobile communication arrangements which include automobile telephones, cellular phones, pagers and GPS (Global Positioning Systems) employ microwave dielectric materials which are required to possess various electrical and physical properties such as, for example, high permittivity (.di-elect cons.), high quality factor(Q), small temperature coefficient of resonance frequency (.tau..sub.f), and good sintering characteristics.
To meet these requirements, U.S. Pat. No. 5,756,412 by the present inventor discloses a novel dielectric ceramic composition having the formula expressed by B'B".sub.2 O.sub.6 (wherein B' is at least one metal selected from the group consisting of Mg, Ca, Co, Mn, Ni and Zn, and B" is one metal selected from the group consisting of Nb and Ta).
Many studies are now being made on the dielectric ceramic compositions that have dielectric properties of high reliability and can be used in a high frequency band above 10 GHz for satellite broadcasting and communication systems. A dielectric ceramic composition used in a high frequency band must have required dielectric properties, e.g., comparably low permittivity of around 20-30, small temperature coefficient of resonance frequency and especially high quality factor, as well as an excellent sintering characteristics.
Based on these requirements, the present inventor studied on the dielectric ceramic compositions having the formula expressed by B'B".sub.2 O.sub.6 (wherein B' is Mg and B" is one metal selected from the group consisting of Nb and Ta) and revealed that such dielectric ceramic compositions have dielectric properties of high reliability in a high frequency band of above 10 GHz.